A certain piece of electrical machinery has exactly three control levers-left (L), center (C), and right (R)-each with positions of...
GMAT Two Part Analysis : (TPA) Questions
A certain piece of electrical machinery has exactly three control levers-left (L), center (C), and right (R)-each with positions of up or down. The machine is able to operate if and only if the operator has placed them in one of the following four configurations.
- L up, C up, R up
- L up, C down, R down
- L down, C up, R up
- L down, C down, R down
Consider the statement, The one and only means of X is Y. Select the options for X and for Y such that the statement, if true, most clearly provides a possible explanation of the above facts.
Phase 1: Owning the Dataset
Argument Analysis Table
| Text from Passage | Analysis |
|---|---|
| "A certain piece of electrical machinery has exactly three control levers-left (L), center (C), and right (R)" |
|
| "each with positions of up or down" |
|
| "The machine is able to operate if and only if..." |
|
| Four configurations listed |
|
Configuration Pattern Analysis
Let me map out the four operating configurations:
- L up, C up, R up → (L and C same, C and R same)
- L up, C down, R down → (L and C different, C and R same)
- L down, C up, R up → (L and C different, C and R same)
- L down, C down, R down → (L and C same, C and R same)
Critical Discovery: In ALL four operating configurations, the C and R levers are always in the same position!
Phase 2: Question Analysis & Prethinking
Understanding the Question Structure
We need to complete: "The one and only means of X is Y"
- This statement structure indicates Y is both necessary AND sufficient for X
- The statement should explain why only those 4 configurations allow operation
Prethinking Based on Our Analysis
Since C and R being in the same position is:
- Present in all 4 operating configurations
- Absent in all 4 non-operating configurations
- The only consistent requirement
Then:
- X should be about making the machine operate (powering on)
- Y should be about placing C and R in the same position
Phase 3: Answer Choice Evaluation
Evaluating Each Choice
For X (what we want to achieve):
- "Powering on the machine" ✓ - This fits perfectly as what we want to do
- "Powering off the machine" - Opposite of what we want
- Lever position options - These would be means, not goals
For Y (the means to achieve X):
- "Placing the L and C levers in the same position" - Not always required (false in configs 2 & 3)
- "Placing the L and R levers in different positions" - Not a consistent pattern
- "Placing the C and R levers in the same position" ✓ - Required in ALL operating configs
- "Placing both the C and R levers in the down position" - Only true for 2 of 4 configs
The Correct Answers
Part 1 (X): "Powering on the machine"
- This is what we want to achieve
- The configurations describe when the machine operates
Part 2 (Y): "Placing the C and R levers in the same position"
- This is the one consistent requirement across all operating configurations
- It's both necessary (must have it) and sufficient (guarantees operation when combined with proper L position)
Common Traps to Avoid
- Focusing on L and C relationship: While L and C are sometimes the same, this isn't consistent across all operating configurations
- Choosing specific positions: Like "C and R both down" - this is too narrow and only covers half the operating states
- Reversing X and Y: Remember X is the goal (powering on) and Y is the means (lever configuration)